1. Field of the Invention
This invention relates generally to a nozzle assembly used for injection molding multilayer or multimaterial articles. More particularly, the invention relates to a nozzle assembly having an inner, middle and outer nozzle. The inner nozzle acts as a manifold for one of the materials whereby a stream of material that enters into the nozzle is split within the inner nozzle into at least two streams of material that form different layers of the injection molded article.
2. Background Art
Multilayer injection molded articles are formed by injecting layers of materials into a mold from a multilayer or multimaterial nozzle assembly. The various materials exit the nozzle assembly and flow into the mold to form separate layers within the mold. One common injection molded multilayer article is a three layer preform that is used to blow mold plastic bottles or containers. The preform can have an inner and outer layer made of the same material, such as polyethylene terephthalate (xe2x80x9cPETxe2x80x9d), and have a middle layer of a barrier material, such as ethylene vinyl alcohol copolymer (xe2x80x9cEVOHxe2x80x9d).
Previous multilayer nozzle assemblies used to make three layer articles have been made with interfitting nozzles made of beryllium copper or steel. The layers of the various materials are kept separate in the nozzles and come together as layers as they exit the nozzle assembly. When the inner and outer layers of the molded article are formed of the same material, the layers are created by splitting a stream of the material in a channel defined between two sections of the nozzle assembly. The two sections of the nozzle assembly that define the split channels are a base or manifold section and an inner nozzle. One problem with these previous nozzle assemblies is that the area where the two sections meet creates leak points. Also, the prior nozzle assemblies require at least four separate pieces, a base, an inner nozzle, a middle nozzle and an outer nozzle. Further, these nozzle assemblies may result in poor seal integrity due to the design of component interfaces and surface flaws caused by cleaning and handling especially between the base and inner nozzle.
The multilayer injection nozzle assemblies of the invention are used to injection mold multilayer articles and comprise an inner, a middle and an outer nozzle. The inner nozzle functions both as a nozzle and as a manifold to split a stream of material into two or more separate streams of material that will form different layers of the injection molded article. The nozzle assemblies of the present invention have reduced leakage and improved performance.
It is one of the principal objectives of the present invention to provide multilayer injection nozzle assemblies that have reduced leakage.
It is another object of the invention to provide multilayer injection nozzle assemblies that can be cleaned easily.
It is still another object of the invention to provide multilayer injection nozzle assemblies that have longer life.
It is a further object of the invention to provide multilayer injection nozzle assemblies that are easy to assemble.
It is still another object of the invention to provide multilayer injection nozzle assemblies that have a reduced number of pieces.
It is further an object of the invention to provide nozzle assemblies containing flow paths that provide equalized pressure to achieve even spill-over around the nozzles.